Heretofore in wide use as motor vehicle evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
To meet such a demand, the present applicant has already proposed an evaporator which comprise a heat exchange core composed of tube groups in the form of two rows arranged in parallel in the direction of passage of air and each comprising a plurality of heat exchange tubes arranged at a spacing, a refrigerant inlet-outlet tank disposed at the upper end of the heat exchange core and a refrigerant turn tank disposed at the lower end of the heat exchange core, the refrigerant inlet-outlet tank having its interior divided by a partition wall into a refrigerant inlet header and a refrigerant outlet tank arranged side by side in the direction of passage of air, the refrigerant turn tank having its interior divided by a partition wall into a refrigerant inflow header and a refrigerant outflow header arranged side by side in the direction of passage of air, the partition wall of the refrigerant turn tank having a plurality of refrigerant passing holes formed therein and arranged longitudinally of the wall at a spacing, the heat exchange tubes of the front tube group being joined at their upper ends to the refrigerant inlet header, the heat exchange tubes of the rear tube group being joined at their upper ends to the refrigerant outlet header, the heat exchange tubes of the front tube group having their lower ends inserted in and joined to the refrigerant inflow header, the heat exchange tubes of the rear tube group having their lower ends inserted in and joined to the refrigerant outflow header, the lower ends of the heat exchange tubes of the two tube groups being positioned above the lower ends of the refrigerant passing holes. A refrigerant flowing into the inlet header of the inlet-outlet tank flows through the heat exchange tubes of the front tube group into the inflow header of the turn tank, then flows into the outflow header through the refrigerant passing holes in the partition wall and further flows into the outlet header of the inlet-outlet tank through the heat exchange tubes of the rear tube group (see the publication of JP-A NO. 2003-75024).
However, various studies conducted by the present inventor have revealed that the following problems are likely to arise owing to the structure of the evaporator disclosed in the above publication wherein the lower ends of the two groups are positioned above the lower ends of the refrigerant passing holes. The refrigerant flowing into the inflow header from the heat exchange tubes of the front tube group is a mixture of liquid phase and vapor phase, and a major portion of the liquid-phase refrigerant flows into the outflow header directly through the refrigerant passing holes and further flows into the heat exchange tubes of the rear tube group. Consequently, the liquid-phase refrigerant and the vapor-phase refrigerant can not be efficiently mixed together inside the inflow header and inside the outflow header, and the air passing through the heat exchange core becomes uneven at different locations.
We have also found that the evaporator disclosed in the above publication is likely to produce superheat in a wide region, elevating the temperature of the air passing through the heat exchange core. In the case where each tube group comprises an increased number of heat exchange tubes, e.g., at least ten tubes, the refrigerant is likely to flow through some of the tubes without becoming completely vaporized. With the evaporator of the above publication, some of refrigerant passing holes formed in a flow dividing plate in the outlet header are located in the same position as heat exchange tubes when seen from above. When the refrigerant passing through such tubes fails to completely vaporize, the refrigerant enters an upper space directly through the refrigerant passing holes and flows into an expansion valve via a refrigerant outlet. The refrigerant not vaporized completely has a lower temperature, which is detected by the expansion value, which in turn diminishes its valve opening, reducing the rate of flow of the refrigerant and resulting in a larger region of superheat. The superheat region of increased area involving inefficient heat exchange leads to impaired refrigeration performance.
Further with the evaporator of the above publication, the refrigerant inlet of the inlet header and the refrigerant outlet of the outlet header are positioned at the same end of the inlet-outlet tank. Alternatively, such inlet and outlet are formed at the longitudinal midportion of the inlet-outlet tank and positioned close to each other longitudinally thereof. We have found that this position of the inlet and outlet is likely to give rise to the following problems. In the course of flow of the refrigerant from the inlet to the outlet, a large amount of refrigerant flows into heat exchange tubes which are included among those of the front and rear tube groups and which are positioned close to the inlet and outlet, entailing the likelihood that a reduced amount of refrigerant will flow through the heat exchange tubes in other locations. For this reason, the paths of flow of the refrigerant through the evaporator become uneven in length, resulting in an uneven pressure distribution and permitting the refrigerant to flow through all the heat exchange tubes at varying rates. As a result, the air passing through the heat exchange core becomes uneven at different locations. The refrigerant tends to flow at nearly the same rate through heat exchange tubes of the front and rear groups at the same position with respect to the left-right direction. In other words, at a position where the rate of flow of the refrigerant through tubes of the front group is small, the rate of flow of the refrigerant through tubes of the rear group at the same position with respect to the left-right direction is also small. Similarly, at a position where the rate of flow of the refrigerant through tubes of the front group is great, the rate of flow of the refrigerant through tubes of the rear group at the same position with respect to the left-right direction is also great. Thus, the amount of refrigerant contributing to heat exchange becomes uneven with respect to the left-right direction of the heat exchange core, with the result that the air passing through the core becomes also uneven in temperature at different locations. While the refrigerant flowing into the inflow header is a mixture of liquid phase and vapor phase, a major portion of the refrigerant of mixed phase flows directly through the refrigerant passing holes into the outflow header and further into the heat exchange tubes of the rear group. The inflow header and the outflow header therefore fail to efficiently mix together the liquid-phase refrigerant and the vapor-phase refrigerant therein, giving the air passing through the core a temperature varying with the location.
In any case, we have found that the evaporator still remains to be fully improved in heat exchange efficiency.
An object of the present invention is to overcome the above problems and to provide a heat exchanger which exhibits excellent heat exchange performance and which achieves a high refrigeration efficiency when used as an evaporator.
In a first embodiment of the heat exchangers, the end portions of the heat exchange tubes inserted in the inflow header project outward beyond the refrigerant passing holes of the partitioning means longitudinally of the tubes, so that the refrigerant portions flowing into the inflow header from the tubes pass over the outer edges, in the longitudinal direction, of the tubes, flow into the outflow header through the holes and are thereby mixed together. Moreover, the refrigerant flowing into the inflow header is unlikely to pass directly through the holes, therefore partly flows inside the inflow header also longitudinally thereof and is agitated at this time. Accordingly, when used as an evaporator, for example, the heat exchanger efficiently mixes the liquid-phase refrigerant portion and the vapor-phase refrigerant portion to result in a generally uniform quality of wet vapor, giving a generally uniformalized temperature to the air passing through the heat exchange core and realizing an improved refrigeration efficiency, i.e., heat exchange efficiency.
In a second embodiment of the heat exchanger, the refrigerant flowing into the inflow header from the heat exchange tubes is prevented from flowing directly into the outflow header through the refrigerant passing holes. This further improves the refrigerant mixing effect described with reference to the first embodiment. Consequently, when used as an evaporator, for example, the heat exchanger efficiently mixes the liquid-phase refrigerant portion and the vapor-phase refrigerant portion to result in a generally uniform quality of wet vapor, giving a generally more uniformalized temperature to the air passing through the heat exchange core and realizing an improved refrigeration efficiency.
In a third embodiment of the heat exchanger, the refrigerant portions flowing into the outflow header through the refrigerant holes are mixed together also inside the outflow header, with the result that when used as an evaporator, for example, the heat exchanger efficiently mixes the liquid-phase refrigerant portion and the vapor-phase refrigerant portion to result in a generally uniform quality of wet vapor, giving a generally more uniformalized temperature to the air passing through the heat exchange core and realizing an improved refrigeration efficiency.
In another embodiment, the function of the partitioning means provided in the heat exchanger described permits the refrigerant to flow through all the heat exchange tubes joined to the inlet header of the inlet-outlet tank at a uniformalized rate, enabling the exchanger to exhibit improved heat exchange performance.
In another embodiment, the partitioning means of the turn tank of the heat exchanger described in par. 6) is integral with the second member. The partitioning means is therefore easy to provide inside the turn tank.
In another embodiment, the heat exchanger described has a refrigerant inlet at one end of the inlet header and a refrigerant outlet at one end thereof alongside the refrigerant inlet. In such a case, the refrigerant portions flowing from the inlet header into the inflow header via heat exchange tubes will not be fully mixed, while the rate of flow of the refrigerant through all the heat exchange tubes of each tube group will be liable to become uneven. Even in this case, however, the exchanger described achieves a high refrigerant mixing efficiency, enabling the refrigerant to flow through all the tubes at a uniformalized rate.
In another embodiment of the heat exchanger, the separating means functions to uniformalize the rate of flow of the refrigerant through all the heat exchange tubes joined to the inlet header, also uniformalizing the rate of flow of the refrigerant through all the heat exchange tubes joined to the outlet header. The heat exchanger therefore exhibits further improved heat exchange performance.
Another embodiment of the invention, serves to reduce the number of components of the overall heat exchanger.
In another embodiment of the heat exchanger, the inlet-outlet tank partitioning means and separating means are integral with the second member. This ensures facilitated work in providing the partitioning means and the separating means in the interior of the inlet-outlet tank.
In an embodiment, the heat exchange tubes of each tube group is at least seven in number, the refrigerant portions flowing from the inlet header into the inflow header through the heat exchange tubes will not be mixed together sufficiently, and the rate of flow of the refrigerant through all the tubes of each group is liable to become uneven. Even in such a case, however, the refrigerant portions can be mixed efficiently, while the refrigerant flows through all the heat exchange tubes at a uniformalized rate.
In another embodiment of the heat exchanger, the refrigerant portions flowing into the inflow header through the heat exchange tubes will not be mixed together sufficiently, and the rate of flow of the refrigerant through all the tubes of each group is liable to become uneven. Even in such a case, however, the structure immediately above ensures efficient mixing of the refrigerant portions, further permitting the refrigerant to flow through all the heat exchange tubes at a uniformalized rate.
In another embodiment of the heat exchanger, the partitioning means is integral with the second member. The partitioning means is therefore easy to provide inside the tank.
Another embodiment of the heat exchanger is reduced in the number of components in its entirety.
Another embodiment ensures facilitated work in providing the partitioning means in the hollow body.
If the heat exchange tubes joined to each of the inflow header and the outflow header are at least seven in number, the refrigerant portions flowing into the inflow header through the heat exchange tubes will not be mixed together sufficiently, and the rate of flow of the refrigerant through these tubes is liable to become uneven. Even in such a case, however, the refrigerant portions can be mixed efficiently, while the refrigerant flows through all the heat exchange tubes at a uniformalized rate.
In another embodiment of the heat exchanger, the refrigerant passing holes in the separating means of the outlet header are positioned between respective adjacent pairs of heat exchange tubes arranged longitudinally of the outlet header and included in the group of heat exchange tubes joined to the outlet header. Accordingly, the refrigerant flowing out of the tubes comes into contact with the separating means without passing directly through the refrigerant holes to flow inside the outlet header also longitudinally thereof. The refrigerant portions flowing out from all the tubes are therefore mixed together. When the exchanger is used as an evaporator, it is likely that the refrigerant will pass through some heat exchange tubes without completely vaporizing and become lower in temperature. Even in such a case, the refrigerant to be admitted into the expansion valve through the refrigerant outlet is given a relatively high uniform temperature since the refrigerant portions from all heat exchange tubes are mixed together. Consequently, a reduction of the expansion valve opening is prevented to avoid the decrease in the flow of refrigerant, diminishing the region of superheat to result in improved refrigeration performance, i.e., improved heat exchange performance.
In another embodiment of the heat exchanger, the refrigerant passing holes are positioned on the upstream side with respect to the direction of flow of air, so that a larger amount of refrigerant flows on the upstream side. This leads to improved refrigeration performance when the exchanger is used as an evaporator, hence a remarkable advantage in the case where the evaporator has a large front-rear width.
When the heat exchange tubes joined to the outlet header are at least ten in number, a wider region of superheat is likely to result if the exchanger is used as an evaporator. Even in such a case, however, the construction described immediately above precludes an increase of the superheat region.
The heat exchanger described in par. 28) can be reduced in the number of components in its entirety.
In another embodiment of the heat exchanger, the separating means and the partitioning means of the inlet-outlet tank are integral with the second member. This results in facilitated work in providing the separating means and the partitioning means in the interior of the inlet-outlet tank.
While the refrigerant admitted into the inlet header from a refrigerant inlet flows to a refrigerant outlet of the outlet header in one embodiment, the refrigerant flowing into the inflow header at the left from heat exchange tubes flows through the left inflow header longitudinally thereof into the outflow header at the right, then flows through heat exchange tubes into the outlet header. On the other hand, the refrigerant flowing into the inflow header at the right from heat exchange tubes flows through the right inflow header longitudinally thereof into the outflow header at the left, then flows through heat exchange tubes into the outlet header and flows out through the refrigerant outlet. Accordingly, the paths of flow of the refrigerant through the heat exchanger are given equal lengths unlike those described in the aforementioned publication, consequently resulting in a uniform pressure distribution and permitting the refrigerant to pass through all the heat exchange tubes at a uniform rate. This uniformalizes the temperature of the air passing through the heat exchange core. In the case where the refrigerant flows through the heat exchange tubes joined to the left inflow header at a reduced rate, and flows through the heat exchange tubes joined to the right inflow header at an increased rate, the rate of flow of the refrigerant through the tubes joined to the left outflow header increases, and the rate of flow of the refrigerant through the tubes joined to the right outflow header decreases. Conversely in the case where the refrigerant flows through the heat exchange tubes joined to the left inflow header an increased rate, and flows through the heat exchange tubes joined to the right inflow header at a reduced rate, the rate of flow of the refrigerant through the tubes joined to the left outflow header decreases, and the rate of flow of the refrigerant through the tubes joined to the right outflow header increases. This uniformalizes the amount of refrigerant contributing to heat exchange with respect to the left-right direction of the heat exchange core, consequently giving a generally uniform temperature to the air passing through the core. Further when the refrigerant as admitted to the left inflow header flows into the right outflow header, and also when the refrigerant flows from the right inflow header into the left outflow header, these refrigerant portions are mixed together efficiently. Accordingly, when used as an evaporator, the heat exchanger efficiently mixes the liquid-phase refrigerant portion and the vapor-phase refrigerant portion to result in a generally uniform quality of wet vapor, giving a generally uniformalized temperature to the air passing through the heat exchange core and realizing a remarkably improved refrigeration efficiency, i.e., heat exchange efficiency.
When the inlet header has a refrigerant inlet at one end thereof, with the outlet header provided with a refrigerant outlet at its one end alongside the inlet end, the evaporator disclosed in the foregoing publication has a marked tendency for a large amount of refrigerant to flow through heat exchange tubes which are positioned in the vicinity of the refrigerant inlet and outlet and included in the front and rear heat exchange tubes, with a reduced amount of refrigerant flowing through the other heat exchange tubes. Even in such a case, the heat exchanger so constructed as described immediately exhibits the advantages described above.
In another embodiment of the heat exchangers, a relatively simple construction is usable for causing the left inflow header to communicate with the right outflow header and the right inflow header to communicate with the left outflow header.
In another embodiment, the heat exchanger can be smaller in the number of components, and can be provided with the partitioning means in the tank with ease.
In the case where each tube group comprises at least seven heat exchange tubes, the evaporator disclosed in the foregoing publication has a strong tendency for a large amount of refrigerant to flow through heat exchange tubes which are positioned in the vicinity of the refrigerant inlet and outlet and included in the front and rear heat exchange tubes, with a reduced amount of refrigerant flowing through the other heat exchange tubes. Even in such a case, the heat exchanger so constructed as described above exhibits the advantages described with reference to the exchanger described above.